As earthquakes go, it was, said Tandis S. Bidgoli, “Enough to cause all the various stakeholders to sit up and take notice.”
Those stakeholders are regulatory agencies, the oil and gas industry, and the public.
A 5.8-magnitude earthquake without foreshocks will do that.
Bidgoli is an AAPG Student/Young Professional member, structural geologist and thermochronologist with the Energy Research section of the Kansas Geological Survey.
About the quake near Pawnee, Okla. the morning of Sept. 3, she said, “Although events of this size are fairly common near plate margins, like in California, they are not a normal occurrence in the mid-continent.”
But it’s getting that way.
As the area experiences more of these quakes and the two states of Kansas and Oklahoma now face the same threat of destructive earthquakes as do Californians, Bidgoli said there has to be a change in the mindset as how they prepare for them.
Cause for Concern, and for New Models
Specifically, she said, because the Sept. 3 earthquake came without warning.
In other large quakes, she explained, there had been smaller foreshocks leading up to the big one. Bidgoli’s worry comes because the recent 5.8 quake was the foreshock.
And if the 5.8 magnitude quake was the foreshock, what else might be coming?
“Our group at the Kansas Geological Survey is working on modeling the pressure field associated with injection in the Arbuckle and evaluating what its relationship is with earthquakes in south-central Kansas,” she said.
Bidgoli, who is also an assistant professor at the University of Kansas, said preliminary results show that seismicity is moving outward from where much of the active disposal is occurring to a greater degree than previously thought.
“Our work suggests that there may be larger hydrodynamic adjustments taking place,” said Bidgoli.
Bidgoli said the potential for problems for places like Kansas (and Oklahoma, for that matter) will be profound and, excuse the expression, structural.
“I grew up in California and was shocked to find so many masonry buildings here in the Midwest. Californians construct their cities, neighborhoods and homes with earthquakes in mind,” she said.
And this seems peculiar to the Oklahoma/Kansas region.
“There are many places where these same technologies have been employed without issues,” she said, and here she mentioned development of the Bakken in North Dakota.
The debates on the causes and effects are fairly well established by now, so that’s not the issue.
“This phenomena of injection-induced seismicity is well known and has been documented in the scientific literature for some time, with one of the most famous examples being the work by Healy and others in 1968 on injection-related earthquakes at the Rocky Mountain Arsenal in Colorado.”
As with most things, though, it’s all in the timing.
“The models we are working on are focused on understanding subsurface pressures and how pressure evolves with time,” Bidgoli explained. “The geologic models incorporate reservoir property data and analyses from wells in Harper and Sumner counties in Kansas, where recent seismicity in the state has been concentrated, and use those properties to simulate fluid flow and pressure changes in the Arbuckle and Precambrian basement. What our preliminary results are showing is that pressures and seismicity are extending beyond areas of concentrated, high-rate disposal. At this time, our analysis suggests that the criteria for what is normally considered an injection induced earthquake, may be more complicated.”
“Frac’ing operations can also induce earthquakes, but the operational window for such activities at a well site is usually short (hours/days) compared to disposal operations (years),” she added.
For a place like Kansas, that’s a new challenge, a new danger.
“Although Kansans are no stranger to natural hazards, the steps you need to take to be prepared for a tornado are very different from those needed for strong ground shaking related to earthquakes. And for Oklahoma and Kansas, we have a combination of factors that play into the current seismicity,” even if the exact dynamic is not yet known.
“We are in unchartered territory when it comes to well management and earthquakes. Some studies, for example a recent paper by McNamara and others on the 2014 Cushing, Oklahoma earthquake sequence, suggest that wastewater reductions can potentially manage seismicity. This conclusion is also supported by the reductions in magnitude 3.0 and greater events in Kansas following state-ordered volume cut-backs,” Bidgoli explained.
These kinds of analyses, she said, must be done on a case-by-case basis because the reservoirs and faults in question are deep underground and their properties are uncertain.
“Factors like a fault’s orientation, the orientation and magnitude of regional stresses, pore pressures and rock properties must be accounted for in an assessment of this kind. For some faults, those not well aligned with crustal stresses, you can inject very large volumes of fluid near them without issue. For others that may be primed for slip, very small changes in pressure can trigger slip and induce earthquakes,” she said.
Risk Management Implications
She said the risks of induced seismicity will increasingly have an effect, not just on public safety concerns, but, obviously, the economic benefits of the oil and gas industry in the way of jobs and revenues. And since activity on one side of the border, say in Pawnee, will affect residents and commerce on the other side, say in Kansas, cooperation is a necessity.
“I think a good starting place is with the media. Our media are powerful agents for information. Beyond that, I think state and local emergency management centers will need to take a proactive role in informing the public on the ways to secure their homes and businesses in the event of a strong earthquake. State leadership should also encourage participation in programs like Great ShakeOut Earthquake Drills, which are organized so that residents, schools and businesses can practice what to do during earthquakes and improve their preparedness.”
“There is no one-size-fits-all approach.”
Bidgoli participated in a National Academy of Sciences, Engineering, and Medicine roundtable in Washington, D.C. in the beginning of December. The focus was on unconventional hydrocarbon development and she was a panelist for a session on induced seismicity, focused on developing strategies to manage risks.